Oil prospecting method



Patente'llbhyalm on. mosrnc'rmo mrmon Millard 8. rural, In, Houston, Tex, a-ignor to Standard Oil Derek poratlon of Delaware pment Company; a car- No Drawing. Application June I, 1939,

Serial No. 277,891

10 Claims.

The present invention i directed to a method tor prospecting for oil. 1/

Some years ago the theory was advanced that hydrocarbon gases difl'use upwardly from petroleum deposits and can be detected in soil gas. This led to the development of the soil gas analysis method of prospecting for petroleum. According to this method soil gas samples are collected and are analyzed by one of several metho s for the presence of hydrocarbons heavier than methane. Since the content of such hydrocar hens in the soil gas, even over a deposit oi petroleum, is quite low, percentages at low as ten parts per million being significant, it is apparent that the method involves much painstaking laboratory work.

More recently it has been discovered thot these s'oil gases diilusing upwardly from petroleum deposits have an efiect on the surface soil, it hovlniz been established'with a considerebledeer'ee oi certainty that these hydrocarbon noses teed oer-=- tain bacteria in the soil, whereby the erristenee 01 o. petroleum deposit can be recognized hr either e their content of such bacterlo in the soil or the presence in the soil of products resulting {from the ieedinet oi sold bacteria upon the hydrocorhon content oi the soil, such products heinr iolrly heavy organic compounds. The priniorr test adopted in the proctlce oi this method o color test. its is known, greet core must he en'ereiserl in the nroctice oi ony method, the results oi which depend upon color tes'm, both in the prope ratlori oi the sample to he tested end in the ohservotion oi? color. letter store could be made loreely iree'irorn error by the use oi photoelectric colorimeters, hut the results were still subject to error on the port or the operotor preparing the samples for color determination.

According to the present invention, the human element is largely eliminated from a method of the general type last described by subjecting the soil samples to the action of gases containing air and hydrocarbons, preferably heavier than methane, and observing the rate or degree of consumption or the hydrocarbons by the soil, this rate or degree depending upon the bacterial con-.

tent of the soil which,-in turn, depends upon the previous history of the soil and particularly upon its relation to petroleum deposits. The practice of the method simply involves the placing of a soil sample in a suitably sealed chamber, preterably transparent, filling the chamber with air and hydrocarbons, and observing the drop in pressure over a selected period of time, the greater the drop, the greater the bacterial content of the soil sample.

Collection oi. soil samples for the practice 0! the present invention is in general the same as 5 that for the soil analysis method previously reterred to. In general, these samples should be collected from undisturbed surfaces; that is, from surfaces which have not been recently plowed or worked over. The preferred procedure includes 10 scraping oil the vegetation from the top of the soil and then taking a sample to a depth not errceeding six inches, including, of course, the surface itself. No special precaution need be observed about sealing the sample or holding adis sorbed or absorbed gases in it, because the re suits of the present invention are not predicated upon the existence or such constituents. To in sure uniformity, however, and to avoid accidental exposure to hydrocarbon otrn'ospheres prior to no testing, it is desirable to pack the samples in cordboord cartons, fruit jars, or the iii-2e, for trerieportotion to the scene oil the test. Oi" course, the present invention contemplates the testing oi soil sornples directly on location, since the or, ripperntus involved is simple end caneasily be corned on o truclz, there being so sensitive ports oi the opparatus which might suffer from joltine in transit.

in order thot the results may be properly" recorded, each sernple is given a number and its loeotion on ii men oi the tree under investigation is noted. Soinpleo may be collected at may do sired intervals. Experience hos demonstroted thnt ten samples to o inlle is n satisfactory spec 53; int, nlthoueh closer or wider spacine; may he iollowed. The samples, tor ease oi location on or men, are preferably collected along straight lines, intersecting each other over the street to he investieated in such a woy as,- to give o. comprelt hensive picture of the area.

Referring specifically to the testing method, each sample is placed in a sealed chamber which is preferably transparent. A gas mixture containing a hydrocarbon, preferably ethane, pro- 4 pane or butane, in admixture with air or oxygen, is fed into the chamber. The gas mixture may contain from five to fifty percent, or more, of hydrocarbon, it being required only that sufllcient air be present for the propagation of the bac- 50 teria which are aerobic. The chamber is originally at atmospheric pressure and is provided with a manometer. If desired, the chamber may be originally at a pressure above atmospheric and provided with pressure gauge.

B The sample is allowed to stand in the hydrocarbon atmosphere for any selected period of time, usuall in excess of about two hours and contains suflicient hydrocarbon, the mercury in the manometer will be sucked into the chamber in due course. 7 V

For uniform results it is of course necessary that all samples be subjected to the same atmos-- phere for the same length of time. The drops in pressure observed with the various samples are then recorded, and the highs are noted on the map of the area under investigation. By drawing lines through locations of samples giving the same pressure drop it is possible to draw a contour map somewhat similar to that which is ordinarily drawn for gravity surveys.

It will be understood that the general principle involved in the present invention can be utilized without following the specific procedure outlined above. For example, the amount of hydroca rbons absorbed or taken up by the soil sample can be determined by analyzing residual gas in the sealed chamber as well as by observing the drop in pressure. Another refinement is to divide each sample into portions and subject one portion to the action of methane, while another portion is subjected to the action of heavier hydrocarbons under the same conditions, the same concentration of hydrocarbons being used in each case. This procedure serves to eliminate errors which might arise by reason of the fact thatthe soil may contain bacteria which have a preferential action on methane. By comparing the results obtained by the action of the respective gases one can determine with certainty the amount of bacteria, contained in the soil sample which is propagated by heavier hydrocarbons.

The nature and objects of the present invention having been thus described, what is claimed as new and useful and is desired to be secured by Letters Patent is:

1. A method for prospecting for petroleum deposits which comprises subjecting samples of the surface soil from spaced points in the area under investiga n to the action of hydrocarbon gas in a seale zone and determining the amount of the hydrocarbon gas taken up by the individual soil samples.

2 A method for prospecting according to claim 1 in which the gas employed is heavier than methane.

3. A method for prospecting for petroleum deposits which comprises collecting spaced samples of surface soil over an areaunder investigation, placing each sample in a sealed zone, filling the zone to a selected pressure with a mixture of air assarza and hydrocarbon gas, and observing the decrease in pressure in said zone with time.

4. A method according to claim 3 in which the gas is a hydrocarbon heavier than methane.

5. A method for prospecting for petroleum deposits which comprises collectin a plurality of samples of surface soil at each of a plurality of points over an area under ingestigation, subjecting at least one sample from each point to the action of an atmosphere containing air and methane, subjecting at least one other sample from the same point to the action of an atmosphere of air and a hydrocarbon gas heavier than methane, and comparing the amounts of the hydrocarbon gases taken up by the samples from different points.

6. In a method of exploration for deposits of hydrocarbon matter, the steps of collecting spaced samples of soil, confining each of said samples in an atmosphere comprising gaseous hydrocarbons, and determining the presence in said sample .of hydrocarbon-consuming bacteria by observing the change in the pressure of the confined atmosphere surrounding said sample.

7. In a method of exploration for deposits of hydrocarbon matter, the steps of collecting spaced samples of soil, confining each of said samples in an atmosphere comprising a gaseous hydrocarbon component, and determining the presence in said sample of hydrocarbon-consuming bacteria by observing the loss of the hydrocarbon component from said atmosphere.

8. In a method of exploration for deposits of hydrocarbon matter, the steps of collecting spaced samples of soil, confining each of said samples in an atmosphere containing hydrocarbons other than methane, and determining the presence in said sample of hydrocarbon-consuming bacteria by observing the loss from said atmosphere of hydrocarbons other than methane.

9. In a method of'exploration for deposits of hydrocarbon matter, the steps of collectin 'samples of soil at different points throughout a region, confining each Of said samples in an atmosphere comprising gaseous hydrocarbons, and determining the relative population density of hydrocarbon-consuming bacteria in said samples by observing the rate of change of the pressure of the confined atmosphere surroundin each sample.

10. A method for prospecting for petroleum deposits which comprises collecting samples of surface soil at spaced points over an area under investigation, placing each sample in a sealed zone, filling the zone with a mixture of air and hydrocarbon gas containing a selected amount of hydrocarbon gas which will be the same for each 8011 sample, permitting this system to stand for a selected period which is the same for each soil sample, and then determinin the amount of hytzirocarbons left in the atmosphere in the sealed one.

MILLARD S. TAGGART, JR. 

